Process of electroslag remelting

ABSTRACT

An ingot casting mould comprises a plurality of superimposed open-ended mould sections each of which includes at least two parts movable horizontally between positions in which they define portions of side walls of an upper reservoir member of the mould and positions in which their inner peripheries define portions of the internal periphery of a mould cavity formed in a lower ingotforming member of the mould, which lower mould member is of smaller cross-sectional area than the upper reservoir mould member.

United States Patent Longbottom Sept. 2, 1975 PROCESS OF ELECTROSLAGREMELTING FOREIGN PATENTS OR APPLICATIONS lnvemori David MelvinLongboflom, South 263,123 1 1927 United Kingdom 164 136 Brlg t NewZealand 1,205,008 9 1970 United Kingdom... 164 52 Assigneez BritishSteel Corporation London 353,796 10/1937 Italy 164/136 England PrtmaryExammerFranc1s S. Husar Flledi 1973 Assistant ExaminerJohn E. Roethel[21] Appl 412,404 Attorney, Agent, or FirmBacon & Thomas 57 ABS ACT [30]Foreign Application Priority Data in 1d TR l r f mgot castmg moucompnses a p ura 1ty 0 super- Nov. 10, 1972 United Kmgdom 52046/72imposed open ended mould Sections each of which in cludes at least twoparts movable horizontally between i 3g positions in which they defineportions of side walls of [58] Field of Search 164/52, 252, 136 f i fmemper olthe d 1n wh1ch the1r lnner perlphenes define portlons of theReferences Cited nternal per1phery of a mould cavity formed n a lowerlngot-formlng member of the mould, WhlCh lower UNITED STATES PATENTSmould member is of smaller cross-sectional area than galllier 164/l theupper reservoir mould member. op ms I 2,388,974 11/1945 Hopkins 164 52 2ClalmS, 15 Drawlng g PATENTEBsEP' 21975 3.902 543 SHEET 2 OF 7 F/G.2. Q

PATEN'FEU 35F 21975 SHEET 3 BF 7 mn sm FIG. 5.

PATENTEDSEP 2191s sum s or? FIGQa.

IIIIIIIII I PATENTED 21975 3,902,543

svan 8 OF Y F/G.70Q.

FIG. 77.

PATENTEUSEP 21% 3,902,543

SHEET 7 9f 7 FIG. 72a.

PROCESS OF ELECTROSLAG REMELTING This invention relates to ingot castingmoulds, more especially, to ingot casting moulds suitable for use in theelectroslag refining process.

In the electroslag refining process an electrically conductive slagwithin a mould is maintained in a molten state and at a temperatureabove the melting point of the metal to be refined. Unrefined metal isintroduced into the mould and is refined as it passes in droplet formthrough a bath of the molten slag, refined droplets collecting to form apool beneath the slag bath. The mould walls and mould base plate arecooled by the circulation of a coolant, normally water, and a solidifiedingot is built up beneath the molten metal pool. The metal to be refinedmay be introduced to the mould in the form of a consumable electrode andthe slag maintained molten by passage of an electric current from theelectrode to the mould base plate.

Hitherto, moulds for use in the electroslag refining process have beenof unitary construction. Such moulds have comprised an upper section forcontaining a bath of molten slag and a lower section of smaller crosssection in which an ingot of refined metal is formed. In order tomaintain the formed ingot within the lower mould section as the ingotbuilds up during operation of the process, it has previously beennecessary either to raise the mould relative to the formed ingot or towithdraw the ingot downwardly from the mould. This relative movementbetween the mould and the ingot has been found to cause defects in thesurface of the formed ingot. The mould which forms the subject of thepresent invention overcomes this disadvantage.

According to the present invention, in one aspect an ingot casting mouldcomprising a plurality of superimposed open-ended mould members each ofwhich includes at least two parts movable horizontally between spacedpositions in which they define portions of side walls of an uppersection of the mould and adjacent positions in which their innerperipheries define portions of the internal periphery of a mould cavityformed in a lower ingot-forming section of the mould, which lower mouldsection is of smaller internal crosssectional area than that of theupper mould section.

According to the present invention in another aspect, a process forproducing an ingot of refined metal comprises the steps of introducingunrefined metal into a bath of molten slag present within a mould whichis constructed of an ascending succession of superimposed open-endedmould members each of which includes at least two parts movablehorizontally between spaced positions in which they form parts of sidewalls of an upper reservoir section of the mould and adjacent positionsin which their inner surfaces cooperate to define part of the innerperiphery of a mould cavity formed in a lower ingot-forming section ofthe mould, passing an electric current through the bath of molten slagto maintain its temperature at a predetermined level, collecting moltenrefined metal in a pool below the slag bath, causing the pool of moltenmetal to solidify to form an ingot within the mould cavity and movingthe parts of said mould members from said spaced positions to saidadjacent positions to maintain the formed ingot within said mouldcavity.

ln the drawings:

FIG. 1 is a side elevation in section of electroslag refining apparatusincorporating a mould in accordance with the invention;

FIG. 2 is a plan view from above of the mould illustrated in FIG. 1;

FIG. 3 is a plan view from above of a further mould in accordance withthe invention;

FIG. 4 is a perspective view of a number of superimposed mould membersconnected to a common coo lant-conveying manifold;

FIGS. 5 and 6 are, respectively, perspective and plan views of a mouldin accordance with the invention for producing two ingotssimultaneously;

FIG. 7 is a plan view of a mould for producing three ingotssimultaneously;

FIG. 8 is a plan view of a mould for producing four ingotssimultaneously;

FIG. 9 is a sectional perspective view of a mould for producing an ingotof variable cross-section;

FIG. 9a is a perspective view of an ingot produced by means of the mouldillustrated in FIG. 9;

FIG. 10 is a sectional perspective view of a mould for producing aroll-shaped ingot with passes;

FIG. 10a is a perspectiveview of an ingot produced by means of the mouldillustrated in FIG. 10;

FIG. 11 is a side elevation in section of a mould in which a roll-shapedingot is being produced;

FIG. 12 is a sectional perspective view of a mould for producing aningot in the shape of a crankshaft; and

FIG. 12a is a perspective view, to an enlarged scale, of an ingotproduced by the mould illustrated in FIG. 12.

The apparatus illustrated in FIGS. 1 and 2 comprises a composite mould 1having an upper reservoir section 2 and a lower ingot-forming section 3of smaller crosssectional area than the upper reservoir section 2; thelower section 3 includes a mould cavity 4. The mould 1 includes aplurality of superimposed plate-like mould members 5 each of, forexample, 1 inch in height; each mould member is divided into two equalwater-cooled parts 5a, 5b which are movable between spaced positions inwhich theydefine portions of opposed side walls of the upper reservoirmould section 2 and adjacent positions in which their inner peripheriesdefine a portion of the periphery of the mould cavity 4. The mouldmembers 5 slide between stationary watercooled side members 6 which,together with the mould members when in their spaced positions, make upthe upper reservoir section 2 of the mould l. The mould members 5 andside members 6 are, preferably, constructed of copper. As mentionedabove, in their adjacent positions the parts 5a, 5b of the members 5together define the inner periphery of the mould cavity 4. Thus, theopposed vertical faces of the parts 5a, 5b are shaped to define therequired contour of the ingot to be formed within the mould. cavity 4.In the mould illustrated in FIG. 2, an ingot of circular cross-sectionis to be formed.

It will be appreciated that by suitable shaping of the opposed verticalfaces of parts 5a, 5b, ingots of different cross-section can beproduced. Thus, in FIG. 3, the opposed faces of the parts 5a, 5b are soshaped that when the parts are in their adjacent positions they togetherdefine a square.

The several mould members 5 which comprise the composite mould 1 areclamped together and, at least initially, the lower end of the mould lis mounted on but insulated from a cooled base plate 7. A consumableelectrode 8 of, for example steel or cast iron, is clamped in anelectrode holder 9 which is movable vertically relative to a mast 10. Asthe refining proceeds, an ingot 11 is built up on the base plate 7; ifan ingot of greater height than the sum of the heights of the respectivemould members is to be produced, one or several mould members 5 mayperiodically be removed from the bottom of the ingot-forming mouldsection 3 and placed on top of those members 5 which define the upperreservoir section 2. For this purpose, the mould 1 is supported byhydraulic jacks 12 which, after one or more members 5 have been removedfrom the bottom of the mould, are raised to bear against the mouldmember now lowermost. In the embodiment illustrated in FIG. 1, the mouldmembers 5 are arranged in groups of five. Electrical current is conveyedto the electrode 8 from a transformer (not shown) connected to themains. The current return path is via a connection made to the baseplate 7.

In operation, electrical current is passed from the electrode 8 to thebase plate 7 to heat by electrical resistance to a temperature at orabove the melting point of the consumable electrode 8 a bath of moltenslag 13 formed in the upper reservoir section 2; the lower end of theelectrode 8 is immersed in the slag bath 13. Droplets of unrefined metalpass from the electrode 8, are refined on passage through and collect ina pool 14 below the slag bath 12. Preferably, the upper surface of themetal pool 14 is maintained at or just below the interface between theupper and lower mould sections 2, 3. As the ingot 11 increases inheight, the parts 5a, 5b of the mould member 5 which defines thelowermost portion of the reservoir section 2 are moved inwardly topositions in which their inner faces meet to define the uppermost mouldmember of the mould cavity 4. In FIG. 1, the parts 5a, 5b of such amember 5 are shown being moved from their spaced to their adjacentpositions. The level of the metal pool 14 may be detected by means of agamma ray source.

In order to maintain a pre-determined distance between the tip of theelectrode 8 and the surface of the metal pool 14, the electrode 8 iscontinuously or periodically raised by the electrode holder 9. Changesin this predetermined distance may be determined by detecting changes inone or more operating parameters.

As the ingot 11 solidifies, those mould members 5 of the loweringot-forming mould section 3 no longer required for cooling and formingthe ingot can be removed from the ingot forming section 3 and placedabove those members forming the reservoir section 2 for subsequentre-use as the level of the slag bath 13 within the section 2 rises andthe height of the ingot 11 increases. As members are removed, the jacks12 are raised. The members 5 may be moved individually or in groups of,say, 5 to 10.

Where an electrode 8 of greater diameter than the internal diameter ofthe mould cavity 4 is employed, the height of each mould member 5 isless than the predetermined distance between the electrode tip and thesurface of the metal pool 14.

Referring now to FIG. 4, the parts of each mould member 5 are connectedby flexible hoses 15 to receive coolant, for example water, from a main16. Coupled between the main 16 and the hoses 15 is a rotatable manifold17 which permits movement of mould sections from the bottom to the topof the composite mould 1 without causing entanglement of the respectivehose connections 15. The hoses 15 may convey coolant to single mouldmembers or, as shown, to a group of mould members.

FIGS. 5 and 6 illustrate a mould by which two ingots can besimultaneously produced. As shown, each part 5a, 5b comprises two sectorshaped portions 18. These portions co-operate with channels 19 formed inthe inner surfaces of the side members 6 to define, in the adjacentpositions of parts 5a, 5b, two mould cavities 4a, 4b. More than oneconsumable electrode may be melted simultaneously within the reservoirsection 2.

FIGS. 7 and 8 illustrate moulds for producing more than two ingotssimultaneously. The mould illustrated in FIG. 7 includes mould members 5which comprise three parts 5a, 5b, 5c and three side members 6. Theparts 5a, 5b, 5c are movable between spaced positions in which, togetherwith the side members 6, they define the upper reservoir mould member 2and closed positions in which their innermost faces meet to define theinner peripheries of three mould cavities being defined by co-operatingvertical semi-circular grooves 20 formed in the inner faces of the sidemembers 6.

The mould illustrated in FIG. 8 is of similar construction to thatillustrated in FIG. 7 except that four mould cavities may be defined byinward movement of four parts 5a, 5b, 5c, 5d, between foursuitably-shaped side members 6.

Additional heating may be supplied to the slag bath within the reservoirmould section 2 to prevent slag freezing within the narrow channelswhich are present when the parts 5a, 5b, 5c, 5d of the mouldsillustrated in FIGS. 7 and 8 are in their spaced positions. Thisadditional heating may be supplied by means of electrical current passedfrom non-consumable electrodes of, for example graphite, immersed in theslag baths which, in use of the moulds, would be present in mouldreservoir sections.

Ingots which vary in cross-section along their length may be produced bymoulds in accordance with the invention. Thus, an ingot 11 asillustrated in FIG. 9a may be produced by means of a mould asillustrated in FIG. 9. This mould includes, sequentially, mould members5 which in their closed positions define a circle, a circle of largerdiameter and a square.

As illustrated in FIG. 10, the inner faces 21 of the mould members 5 maybe inclined to the vertical to produce, for example, passes 22 in aroll-shaped ingot. Such an ingot is illustrated in FIG. 10a. The necks23 of the roll-shaped ingot are produced by positioning mould membershaving central apertures of small diameter below and above membershaving central apertures of greater diameter, which latter membersdefine the desired surface of the roll barrel 24.

As illustrated in FIG. 11, for forming the upper journal of aroll-shaped ingot, the parts 5a, 5b of a mould member having a centralaperture conforming to the required journal diameter are moved acrossthe interface of the two mould sections 2,3 when the level of the metalpool 14 is below (for example, one-half inch below) the interface.Molten slag is consequently trapped below the journal mould member; thisslag solidifies to form a heat insulating crust 25 to prevent shrinkageof the top surface of the barrel of the roll-shaped ingot which mightotherwise be caused by overcooling.

In FIG. 12, there is illustrated a mould for forming an ingot in theshape of a crankshaft; such an ingot is illustrated in FIG. 12a. Themould comprises lower and upper mould members which define mouldcavities for forming, respectively, lower and upper journals 26separated by a stationary enlarged mould member 27 which defines theintermediate web 28 of the crankshaft. In this embodiment, molten metalfrom a consumable electrode initially solidifies within the lower mouldcavity to form the lower journal; the metal is then allowed to enter theintermediate stationary mould member 27 and solidifies within thesection to form the web 28 of the ingot. More than one consumableelectrode may be melted at this stage. Alternatively, one or morenon-consumable electrodes may be employed to provide additional heatingwithin the enlarged mould cavity. Once the web has been formed, theupper mould members are moved to their closed positions to define themould cavity for the upper journal of the ingot. More than one web maybe formed by providing further web and journal-forming mould members.The web-forming mould members may be angularly displaced about the axisof the web member from one another.

The upper surface of each mould member described hereinbefore may beconcave towards its central opening so that when positioned at the topof the ingotforming section 3, molten metal is encouraged to flow intothe mould cavity 4.

The invention offers the advantage over prior proposals for mouldshaving reservoir and ingot-forming sections of different cross-sectionthat no relative movement occurs between the mould and the ingot, thusensuring a good surface to the ingot.

I claim:

1. In a process for progressively producing an ingot of refined metal byremelting a consumable electrode of the metal to be refined within abath of electrically conductive molten slag located in an open endedmould, which mould includes an upper reservoir section for containingthe molten slag bath and a lower section including a mould cavity ofsmaller crosssectional area than the upper section in which thesolidified ingot is formed, the steps of constructing the mould from anascending succession of superimposed open ended mould members each ofwhich includes at least two parts movable horizontally in slidingcontact with stationary side members between spaced positions in whichthe parts together with the side members define the walls of the upperreservoir section of the mould and adjacent positions in which the innersurfaces of the parts co.-operate to define the inner periphery of amould cavity of the lower mould section; providing a bath ofelectrically conductive molten slag in the reservoir section of themould; inserting a consumable electrode .of unrefined metal having incrosssection a linear dimension larger than the smallest lineardimension of the ingot to be produced into the molten slag bath; passingan electric current through the molten slag bath to maintain itstemperature at or above the melting point of the consumable electrode tocause droplets of metal to melt off from the electrode and to passthrough the slag bath and collect in a pool below the slag bath; causingthe molten metal progressively to solidify to form a refined ingotwithin the mould cavity; moving the parts of the spaced mould membersimmediately above the mould cavity horizontally from their spacedpositions to their adjacent positions to form, above said mould cavityand below said molten slag bath, a further mould cavity; and permittingthe molten metal in the: further mould cavity to progressively solidify.

2. A process according to claim 1 in which the height of each mouldsection is less than the distance between the lower end of theconsumable electrode and the surface of the pool of molten metal.

1. IN A PROCESS FOR PROGRESSIVELY PRODUCTING AN INGOT OF REFINED METALBY REMELTING A CONSUMALE ELECTRODE OF THE METAL TO BE REFINED WITHIN ABATH OF LECTRICAL CONDUCTIVE MOLTEN SLAG LOCATED IN AN OPEN ENDED MOULD,WHICH MOULD INCLUDES AN UPPER RESERVOIR SECTION FOR CONTAINING THEMOLTEN SLAG BATH AND A LOWER SECTION INCLUDING A MOULD CAVITY OF ASMALLER CROSSSECTIONAL AREA THAN THE UPPER SECTION IN WHICH THESOLIDIFIED INGOT IS FORMED, THE STEP OF CONSTRUCTING THE MOULD FROM ANASCENDING SUCCESSION OF SUPERIMPOSED OPEN ENDED MOULD MEMBERS EACH OFWHICH INCLUDES AT LEAST TWO PARTS MOVABLE HORIZONTALLY IN SLIDINGCONTACT WITH STATIONARY SIDE MEMBERS BETWEEN SPACED POSITIONS IN WHICHTHE PARTS TOGETHER WITH THE SIDE MEMBERS DEFINE THE WALLS OF THE UPPERRESERVOIR SECTION OF THE MOULD AND ADJACENT POSITIONS IN WHICH THE INNERSURFACES OF THE PARTS CO-OPERATE TO DEFINE THE INNER PERIPHERY OF AMOULD CAVITY OF THE LOWER MOULD SECTION, PROVVIDING A BATH OFELECTRICALLY CONDUCTIVE MOLTEN SLAG IN THE RESERVOIR SECTION OF THEMOULD, INSERTING A COMSUMABLE ELECTRODE OF UNREFINED METAL HAVING ACROSS-SECTION A LINEAR DIMENSION LARGE THAN THE SMALLEST LINER DIMENSIONOF THE INGOT TO BE PRODUCE INTO THE MOLTEN SLAG BATH, PASSING ANELECTRIC CURRENT THROUGH THE MOLTEN SLAG BATH TO MAINTAIN ITSTEMPERATURE AT OR ABOVE THE MELTING POINT OF THE CONSUMABLE ELECTRODE TOCAUSE DROPLETS OF METAL TO MELT OFF FROM THE ELECTRODE AND TO PASSTHROUGH THE SLAG BATH AND COLLECT IN A POOL BELOW THE LAG BATH, CAUSINGTHE MOLTEN METAL PROGRESSIVELY TO SOLIDIFY TO FORM A REFINED INGOTWITHIN THE MOULD CAVITY, MOVING THE PAFRTA OF THE SPACED MOULD MEMBERSIMMEDIATELY ABOVE THE MOULD CAVITY HORIZONTALLY FROM THEIR SPACEDPOSITIONS TO THEIR ADJACENT POSITIONS TO FORM. ABOVE SAID MOULD CAVITYAND BELOW SAID MOLTEN SLAG BATH, A FURTHER MOULD CAVITY, AD PERMITTINGTHE MOLTEN METAL IN THE FURTHER MOULD CAVITY TO PROGRESSIVELY SOLIDIFY.2. A process according to claim 1 in which the height of each mouldsection is less than the distance between the lower end of theconsumable electrode and the surface of the pool of molten metal.